我的ajax post方法有效但我无法通过php捕捉到它的价值

post method , it can post value, my success alert is working but i can not echo in my php. i tried to send to same page and another page. Both they haven't work. Here is my ajax code :

<script>$( "#il" ).change(function() {

        var aa = $("#il").val();
        $.ajax({
           url: 'never.php',
           type: 'POST',
           data: { aa1 : 'mynameis'},
           success: function () {
           alert($("#il").val());
              },

        });
        });

</script>   

and here is my php code to catch :

<?php   

       $aa = $_POST['aa1'];

       if($aa != ""){

                echo $aa;

            } else { echo "puuf";}
?>

In order to catch the data returned from the PHP echo you need to add a parameter to the success method for javascript to place the value in for you to then make use of

<script>
$( "#il" ).change(function() {

    var aa = $("#il").val();
    $.ajax({
            url: 'never.php',
            type: 'POST',
            data: { aa1 : 'mynameis'},
            success: function (data) {
    //  -  -  -  -  -  -  -  - ^^^^
                alert($("#il").val(data));
    //  -  -  -  -  -  -  -  -  -  ^^^^
            }
        });
});
</script>   

You'll have to define a data parameter on the success callback, because the echoed data have to be passed as argument to it. So,

The client script:

<script type="text/javascript">
    $("#il").change(function () {
        var aa = $("#il").val();

        $.ajax({
            url: 'never.php',
            type: 'POST',
            data: {
                aa1: 'mynameis'
            },
            success: function (data) {
                alert(data);
            },
        });
    });
</script>

And the PHP:

<?php
$aa = $_POST['aa1'];

if (isset($aa) && !empty($aa)) {
    echo $aa;
} else {
    echo "puuf";
}
?>